Field of the Invention
The present invention relates to a power supply system, a power transmission device, a power receiving device, a method for controlling the power transmission device, a method for controlling the power receiving device, and a program.
Description of the Related Art
There are four systems for supplying power in a non-contact manner (wirelessly): an electromagnetic induction system; a magnetic field resonance system; an electric field coupling system; and an electromagnetic wave reception system. In recent years, a magnetic field resonance system has drawn attention among the four systems in that it can transmit a sufficiently large amount of power with a long transmission distance. In the magnetic field resonance system, there has been proposed a “1 to N” (where N is a plural number) power supply system in which a power transmission device transmits power to a plurality of wireless power receiving devices, taking advantage of this long transmission distance (refer to Japanese Patent Application Laid-Open No. 2009-136132, for example).
In the configuration of Japanese Patent Application Laid-Open No. 2009-136132, the power transmission device transmits a certain pulse signal, while it is in a standby mode where the power transmission device does not supply power, to search for any wireless power receiving device approaching the power transmission device within several meters therefrom. If any wireless power receiving device transmits its unique ID to the power transmission device, the power transmission device determines whether the wireless power receiving device is a power supply target. If the wireless power receiving device is a power supply target, the power transmission device transmits power to the wireless power receiving device. At this point, the power transmission device can transmit a unique code to the wireless power receiving device to individually receive an amount of charge and a state of the device from the wireless power receiving device.
In the above configuration, the shorter the distance between the power transmission device and the power receiving device, the higher the transmission efficiency of power. However, it is difficult for the user of the power receiving device to know at which position the power receiving device can receive power at a good transmission efficiency.